Lignocellulosic composite boards, such as oriented strand board (“OSB”), flake boards, wafer boards, wood particle boards, and the like are generally formed of wood “flakes” or “strands” bonded together by a resin binder under heat and compression to provide a unitary board structure. For OSB boards, for instance, the wood flakes are made by cutting logs into thin slices with a knife-edge oriented parallel to the length of a debarked log. The cut flakes are broken into narrow strands generally having lengths oriented parallel to the wood grain that are larger than the strand widths.
In one fabrication arrangement for making such composite boards, the green wood flakes are dried to remove water to a level more conducive for subsequent processing. For instance, dried flakes are easier to handle and process in subsequent coating operations in which a thin layer of binder and sizing agent is applied to them before board consolidation operations.
In one arrangement, the green wood flakes are dried in a large industrial forced-air dryer, and then are conducted to a cyclone as a wood piece-laden gas. The cyclone is used to separate the dried wood flakes from the transport gas, which is usually air.
A cyclone comprises a hollow body defining an interior space having a cross-section that tapers inward towards the bottom. Cyclones are often constructed with an upper cylindrical portion and a lower frustoconical portion. A gas having entrained solid particles enters via a tangential or involute inlet towards the upper end of the cyclone body and passes out through an outlet near the bottom end of the cyclone body. The geometry of the cyclone body induces helical downward spiral flow of the wood piece-laden gas inside the cyclone in a radially inner region of the interior space. The gas flow changes direction near the bottom of the cyclone, and an air core spirals upwardly through a radially central region of the space inside the cyclone. The spirally flow of the gas applies a centrifugal force to particles entrained and suspended within the gas and exerts differing forces on the particles depending on their size and/or specific gravity. In general, heavier or larger particles are radially displaced towards the radially outer region of the interior space of the cyclone body, while gas, and very fine particles if present, tend to gravitate towards a radially central region of the interior space from where they are carried upwardly with the air core which flows out through the gas exhaust outlet of the cyclone body.
Ideally, the cyclones are operated continuously and should provide a steady controlled rate of flakes settling at the discharge end of the cyclone body where they can be collected and discharged from the cyclone in an orderly fashion for subsequent processing. Newly installed cyclone systems that are operated within original appropriate design specifications and associated conditions generally can operate in that manner. Conventional cyclone arrangements have not been equipped with built-in means to handle the occurrence and presence of large clumps of flakes or other solid materials inside the cyclone during a production run which may clog or jam up narrower sections or components of the cyclone.
However, the present investigators have observed that cyclones that have already been in use for some period of time and/or cyclones which encounter abnormal or significant sudden fluctuations in operating conditions can be at risk of large masses of flakes entering or forming inside the cyclone that plug up the narrowed bottom part of a conventional cyclone separator.
The present invention addresses a need for improvements in cyclone separator technology, especially for retrofitting existing systems already in use and/or systems susceptible to operated outside design or normally expected conditions, whereby flake or particle plugs can be prevented from forming within cyclones during operation, which in turn eliminates production delays and costs associated with removing such plugs from a cyclone.